Percutaneous oxygenators have been described in the prior art for more than twenty years. As disclosed in U.S. Pat. No. 4,911,689 to Hattler, a percutaneous oxygenator comprises a number of hollow, gas-permeable fibers. This device is inserted through a single small incision into a patient's venous system. When an oxygen supply is attached to the device, oxygen flows through the hollow fibers and diffuses through the wall of the fibers into the patient's blood. Conversely, carbon dioxide from the blood diffuses back across the fiber wall, up the fibers and out of the system to the atmosphere. While improvements to this design have been made, to date, no percutaneous oxygenator is able to fully provide the necessary oxygenation required. At best performance, prior art oxygenators may supply 50%-70% of required metabolic oxygen. Therefore, it has been proposed that percutaneous oxygenators may be used to augment natural patient respiration or mechanical ventilation support already provided to the patient through the patient's airway. The augmentation of the natural patient respiration may allow a patient to avoid mechanical ventilation. For a patient who is already receiving mechanical ventilation support, the introduction of percutaneous oxygenator support would reduce the demand for aggressive ventilatory treatment. This is desirable due to the fact that aggressive ventilatory treatment may cause lung injury or increase the cardiac stresses on the patient.
Percutaneous oxygenator technology is not limited in scope to merely the delivery of supplemental oxygen. The same catheterization technique of the patient with gas-permeable membrane fibers can be used to deliver a variety of medical gases intravenously into the patient's blood stream. This technique may be used to deliver anesthetic agent, or other medical gases such as carbon dioxide (CO2), nitrogen (N), nitrous oxide (NO), or helium (He).
Typically, when a patient is receiving ventilatory support, the effectiveness of this support is monitored using a spirometer and respiratory gas monitor such as the Datex-Ohmeda S5 Gas Analyzer. The data collected from the spirometer and gas monitor is used to monitor the composition, flow rates, and exchange rates of the gases inspired and expired by the patient. However, patients receiving mechanical ventilatory support often have compromised gas exchange in their lungs. A patient receiving supplemental percutaneous oxygenator support often results in the erroneous prediction or estimation of the patient's blood gas concentration due to mismatched blood-gas exchange and compromised gas diffusion across the alveoli. Solutions to this problem have been invasive and time-consuming. Typically, blood samples must be drawn intermittently and individually analyzed to assess the patient's actual blood gas concentration and evaluate the adequacy of the combined treatment. While systems have been developed to automatically sample and analyze the patient's blood gas concentration, such as that disclosed in U.S. Pat. No. 4,516,580 to Polanyi, these systems require the invasive arterial insertion of a costly multi-parameter, multi-sensor transducer.
Despite improvements, all of the aforementioned systems are limited in their ability to continuously monitor a patient's blood gas concentration. All of these systems and methods require the taking of an actual blood sample. This inherently reduces the sampling rate of the patient's blood and additional time is required to compute the blood gas concentration. These delays produce a lag time that can inaccurately display the patient's blood gas concentration.
It is therefore desirable for a system by which the blood gas concentration of a patient receiving both mechanical ventilation and percutaneous oxygenator support may be determined without the introduction of an invasive intravascular transducer. It is also desirable for a system by which components already used in conjunction with or associated with the mechanical ventilation and/or percutaneous oxygenation of a patient are used to determine patient blood gas concentration.